1. Field of the Invention
The present invention relates to a method and apparatus for transferring data between a disk and a central processing unit (CPU) in general and to a method and apparatus for transferring data between a disk and a CPU comprising toggling dual header and dual data buffers in particular.
2. Description of Prior Art
Data stored on a disk is typically stored in a plurality of addressable sectors which are located in a plurality of concentric tracks.
To transfer data to or from the disk in a conventional manner, a CPU transfers a header to a disk controller (DC). The header contains information about the sector including its address or location on the disk. After receiving the header, the disk controller accesses the sector and transfers the data between the CPU or an intermediate data buffer and the disk.
Each of the steps involved in accessing and reading data from or transferring data to a sector on a disk takes time. Additonal time is required when the data being transferred to or from a disk is subjected to error detection and correction procedures.
In relatively simple disk storage systems, the time required to address a sector, allow the addressing circuits to stabilize, retrieve data from or transfer data to the sector on the disk and to check the data for errors generally prevents the accessing of physically adjacent sectors within a single revolution of the disk.
Apparatus capable of accessing physically adjacent sectors on a disk within a single revolution of the disk have been proposed; however, they are generally unsatisfactory for one reason or another. For example, in one such prior known apparatus, all sectors in a track are read by simply addressing the track and commencing the reading of the sectors upon the detection of an index mark on the track. In this apparatus, header information is not used and therefore the time required to set up and stabilize the sector addressing circuits is not required. However, because sectors are not individually addressed, conventional data processing, such as error detection and correction, is generally not possible or is impractical.
In another prior known scheme, a plurality of non-toggling header and data buffers are used for individually addressing successive sectors in a track. However, in this scheme extra control lines and tracking information is required to be processed in order to synchronize the disk controller with the disk and the CPU operations.